It is well known that peroxygen bleaching agents, e.g., perborates, percarbonates, perphosphates, persilicates etc., are highly useful for chemical bleaching of stains found on both colored and white fabrics. Such bleaching agents are most effective at high wash solution temperatures, i.e., above about 60.degree. C. to 70.degree. C. In recent years, attempts have been made to provide bleaching compositions that are effective at lower wash solution temperatures. In consequence, there has been much industrial research to develop substances generally referred to as bleach activators, that render peroxygen bleaches effective at bleach solution temperatures below 60.degree. C. These low temperature bleaches are useful in a variety of products intended for use under machine or hand-wash conditions, e.g., additive pre-additive or soak-type laundry compositions as well as all-purpose detergent compositions.
A bleach activator can generally be described as an organic peroxy acid bleach precursor which in the bleaching solution reacts with an inorganic peroxygen bleaching agent with release of the organic peroxy acid. Many such bleach activators are known in the art, most of which contain perhydrolysable N-acyl or O-acyl residues. Examples of these include succinic, benzoic and phthalic anhydrides, tetracetylethylene diamine and tetracetylglycouril, all of which are water-insoluble materials to varying degrees.
Water-soluble bleach activators are also known in the act and are described in detail in, for example, U.S. Pat. No. 4,412,934 and European Patent Application No. 84301070.3. These activators have a number of advantages over water-insoluble materials including rapid dispersibility in wash or bleach solution and also the ability to exhibit surface bleaching. On the downside, however, water-solubility greatly exacerbates activator stability problems resulting from interaction with moisture and peroxygen bleaching agent during prolonged storage in the bleach or detergent composition.
It is also known in the art to incorporate bleach acctivators in a detergents slurry for spray-drying (see GB-A-1540832) whereby the resulting detergent composition comprises the bleach activator homogeneously distributed therein. In the case of water-soluble bleach activators, however, it is found that the conventional crutching and spray-drying process results in essentially complete degradation of the activator.
It has now been found, however, that water-soluble bleach activators can be successfully crutched and spray-dried by incorporating an inorganic hydratable material in the crutcher slurry mix and adjusting the pH of the slurry to within the range from about 3 to about 8 prior to spray-drying. Moreover, the subsequent granule is found to combine excellent stability characteristics when stored in a detergent or bleach composition, as well as improved dispersibility on addition to the wash or bleach solution.